1. Field of the Invention
The present invention relates to an azomethine dye precursor as a useful novel compound.
Further, the present invention relates to a single-color or multicolor image-forming material containing the azomethine dye precursor and an image-forming method using the image-forming material.
2. Description of the Related Art
Heretofore, various dry-type image-forming methods that do not use a liquid developing agent and the like and do not produce wastes have been studied. Among these methods, a method, which uses a light-hardenable composition as a component of the image-forming layer of a recording material (an image-forming material), has been the focus of much attention.
This method is characterized in that the exposure to light causes the composition that hardens on exposure to light contained in the image-forming layer to harden and thereby form a latent image, while the component, contained in the unexposed portions of the image-forming layer which contributes to the color-developing reaction, is transferred by heat or pressure within the image-forming layer to thereby form a colored image. When a recording material based on such a method is used, the process comprises exposing the image-forming material to light through an image original to thereby form a latent image by hardening the exposed portions, and applying heat or pressure to the recording material to thereby cause the component, contained in unhardened portions (unexposed portions) and which contributes to the color development reaction, to move so as to form a visible image.
Conventionally known as such a recording material is a recording material which is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 61-123838 and which is formed by laminating the following: a layer containing a photopolymerizable composition composed of a vinyl monomer having an acidic group and a photopolymerization initiator; an isolating layer; and a layer composed of an electron-donating colorless dye. In the case of this recording material, since the thermal diffusion of the acidic group does not occur in the non-image portions, i.e., portions hardened by photopolymerization, the non-image portions are free from a coloration problem. However, the problem of this recording material is that the density of the developed color is low and the durability is low.
Recording materials, in which the low density of developed color is improved, include the recording materials described in JP-A No. 3-87827 and JP-A No. 4-211252. The former is a two-component, photo- and heat-sensitive, color-developing recording material in which one of the two components is enclosed in microcapsules while the other component is contained outside the microcapsules (1) as a hardenable compound of the composition which hardens on exposure to light or (2) together with the composition which hardens on exposure to light. The latter is a photo- and heat-sensitive recording material comprising a support having thereon a layer having microcapsules enclosing an electron-donating colorless dye and a composition which hardens on exposure to light containing an electron-accepting compound, a polymerizable vinyl monomer, and a photopolymerization initiator outside the microcapsules. However, none of these two recording materials reached a fully satisfactory level in terms of durability of images because an electron-donating colorless dye, i.e., a so-called phthalide compound, was used as the dye precursor.
Likewise, recording materials, described in Japanese Patent Application Publication (JP-B) Nos. 64-7378, 64-7377, 64-7376, and so on, are known as examples of photo- and pressure-sensitive paper. However, none of these recording materials reached a fully satisfactory level in terms of durability of images because the dye precursors used in these recording materials were also phthalide compounds.
JP-B No. 5-42359 discloses a thermal image-forming method in which images can be formed by heating image-wise, a recording material having in the image - forming layer thereof a compound having a thermally unstable carbamate moiety and capable of causing an irreversible monomolecular fission, to thereby cause the compound to thermally decompose and undergo a visible change image-wise. Although a dye precursor besides a phthalide compound can also be used in this method, since the image-wise color development is carried out by heat alone, this method is associated with the following problems. The problems are that, since a large amount of heat is required when images are written, the apparatus is necessarily large and the processing speed is slow and that fogging tends to occur in non-image portions due to remaining heat or accumulated heat derived from the writing step. Another problem is a storability problem that, since the color development is controlled by heat alone, fogging tends to occur during storage.
Japanese Patent No. 2744101 describes a heat-sensitive element which forms images when heated image-wise and which comprises a dye precursor substituted by a blocking group that can be thermally removed when heated and a leaving group that irreversibly leaves when heated. This heat-sensitive element is also associated with problems similar to those of the thermal image-forming method described in JP-B No. 5-42359 because the color developability is controlled by heat alone. Another problem is a storability problem that, since the developed color is not fixed, the dye precursor is gradually decomposed in the white background portions (non-image portions) and fogging tends to occur, for example, under a thermally enforced condition.
Accordingly, a dye precursor, which develops color by an element other than heat or by the action of heat and an element other than heat, is desired.
Further, JP-A No. 5-204087, PCT National Publication No. 8-507885, and PCT National Publication No. 10-502460 disclose photo- and heat-sensitive photographing materials using dye precursors. However, since these materials use silver halides as a photosensitive material, a need exists for an image-forming material capable of forming images in a perfectly dry processing system without using silver halides (hereinafter referred to as xe2x80x9cnon-silver saltxe2x80x9d system) from the standpoint of storability, ease in handling, etc.
An object of the present invention is to provide an azomethine dye precursor as a useful novel compound which can develop color by the action of a deblocking agent or by the action of heat and a deblocking agent and which, when used in the image-forming layer of an image-forming material, exhibits good color development by a small amount of energy and provides images having very good durability.
Another object of the present invention is to provide a single-color or multicolor image-forming material capable of forming high-quality and highly durable images in a rapid way in a perfectly dry processing system, which does not require a developing solution or the like and does not produce wastes, and to provide an image forming method using the image-forming material.
The objects described can be achieved by the present invention described below. That is, the first aspect of the present invention is an azomethine dye precursor represented by the following general formula (1): 
In the general formula (1), Ar represents an aromatic ring which may have a substituent or a heterocycle; and X represents a bivalent group linking a carbon atom and a nitrogen atom. Cp represent a coupler residue which may or may not form a ring.
The second aspect of the present invention is an image-forming material comprising a support having thereon an image-forming layer containing at least one deblocking agent and at least one azomethine dye precursor represented by the following general formula (1): 
wherein Ar represents an aryl group or a heterocyclic group which may each have a substituent; X represents a bivalent group linking a carbon atom and a nitrogen atom; and Cp represent a coupler residue which may or may not form a ring.
The third aspect of the present invention is an image-forming method comprising the steps of:
(a) forming an image-forming material by disposing an image-forming layer on a support, with the image-forming layer containing at least one deblocking agent and at least one azomethine dye precursor represented by the following general formula (1): 
wherein Ar represents an aryl group or a heterocyclic group which may each have a substituent; X represents a bivalent group linking a carbon atom and a nitrogen atom; and Cp represent a coupler residue which may or may not form a ring;
(b) producing a visible image by heating and/or pressing the image-forming material.
The azomethine dye precursor of the present invention produces an azomethine dye (i.e., develops a color) by the action of a deblocking agent at room temperature or in a temperature range in which the azomethine dye precursor does not develop a color on its own by being heated alone unless a deblocking agent is present. The use of the azomethine dye precursor of the present invention in an image-forming layer of the image-forming material enables the image-forming material to develop a good color using a small amount of energy, imparts high sensitivity, and raises durability such as storability of the images obtained to a very good level.
Unlike an image-forming material and an image-forming method using a dye precursor which develops a color by heat alone, the image-forming material and the image-forming method of the present invention, which uses a novel azomethine dye precursor capable of developing a color when brought into contact with a deblocking agent, has a high sensitivity and can rapidly form a high-quality and highly durable image whose non-image portions are less likely to produce fogging. If necessary, at least one photopolymerization initiator and at least one polymerizable compound may be incorporated in the image-forming layer; and this incorporation enables the image-forming layer to have high sensitivity to light and to provide highly durable images having a good hue. Furthermore, if necessary, the thus-obtained image, including image portions and background portions (non-image portions), may be polymerized; and this polymerization can fix the image and thus raise the durability to a higher level.